1. Field
Exemplary embodiments of the present invention relate to a visible color noise reduction technology in an image sensor, and more particularly, a 4-color pixel image sensor having visible color noise reduction function in a near infrared ray (IR) pixel that reduces a visible color noise in a visible region and a near IR (NIR) region of a 4-color pixel image sensor having a red pixel a green pixel, a blue pixel and an IR pixel.
2. Description of the Related Art
An image sensor is an element for converting an optical image into an electrical signal, and is widely used in a digital camera, a smart phone, an industrial equipment and a medical equipment.
As shown in FIG. 1A, a conventional 3-color pixel image sensor includes an active pixel array region 110A and a visible optical black pixel region 120A.
The active pixel array region 110A includes a plurality of unit pixels (active pixels) of a red color (R), a green color (G) and a blue color (B), which are arrayed in a matrix shape, and outputs a photoelectric converted image signal of 3-color. Each of the plurality of unit pixels includes a photoelectric conversion transistor, a charge detection element, a charge transfer transistor, a reset transistor and a selection transistor.
Since the visible optical black pixel region 120A is arranged to be adjacent to a side of the active pixel array region 110A and a pixel output is used as an offset value in a dark state, the visible optical black pixel region 120A is implemented in a state of the cut-off of an incident light. That is, the visible optical black pixel region 120A includes a black pixel which maintains a black level using a cutoff pixel and adjusts a pixel output by selectively being driven to compensate for the black level.
Like this the visible optical black pixel region 120A reduces a noise by determining an offset value of a corresponding active pixel using a plurality of unit pixels having a same structure as the active pixel included in the active pixel array region 110A and having a structure where the incident light is cutoff by a metal layer.
As shown in FIG. 1B, a conventional 4-color pixel image sensor includes an active pixel array region 110B and a visible optical black pixel region 120B.
The active pixel array region 110B includes a red pixel, a green pixel a blue pixel and an IR pixel, and outputs a photoelectric converted image signal of 4-color.
The visible optical black pixel region 120B outputs a constant reference signal irrespective of the incident light by having the plurality of unit pixels of structure where the incident light is cutoff by a light shielding layer in a region adjacent to the active pixel array region in order to prevent a level of an image signal from being changed according to a peripheral temperature variation.
Like this, the conventional 4-color pixel image sensor including only a visible optical black pixel region may conceal a color noise of a visible wavelength, but may not compensate for a noise (or cross talk) transferred from a RGB unit pixel to an NIR pixel and deteriorate a characteristic of the IR pixel.